<template>
    <ul class="list">
        <li class="item" 
        v-for="item of letters" 
        :key="item"
        :ref="item"
        @touchstart="handleTouchStart"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd"
        @click="handleLetterClick"
        > 
        {{item}}
        </li>
    </ul>
</template>

<script>
export default {
    name:'CityAlphabet',
    props:{
        cities : Object
    },
    computed : {
        letters () {
            const letters = []
            for (let i in this.cities){
                letters.push(i)
            }
            return letters
        }
    },
    data () {
        return {
        touchStatus: false,
        startY: 0,
        timer: null
    }
    },
    updated () {
        this.startY = this.$refs['A'][0].offsetTop
    },
    methods:{
        handleLetterClick(e){
            this.$emit('change',e.target.innerText)//向外触发事件
        },
        handleTouchStart () {
            this.touchStatus = true
        },
        handleTouchMove (e) {
            if(this.touchStatus){
                if(this.timer){
                    clearTimeout(this.timer)
                }
                this.timer = setTimeout(() => {
                const touchY = e.touches[0].clientY - 79
                const index = Math.floor((touchY - this.startY) / 20)
                if(index >=0 && index<this.letters.length){
                this.$emit('change',this.letters[index])
                }
                }, 16)

            }
        },
        handleTouchEnd () {
            this.touchStatus = false
        }
    }
}
</script>

<style lang='stylus' scoped>
@import '~styles/varibles.styl'
    .list
        display :flex
        flex-direction :column
        justify-content :center
        position :absolute
        right :0
        top :1.58rem
        bottom :0
        width :.4rem
        .item
            line-height :.44rem
            text-align :center
            color :$bgColor

</style>
